"People who occupy these types of positions, where they have the welfare and security of the nation in their hands, have a special obligation to not do anything that might create a problem," said Judge Walton.

A tough sentence for Libby was unfair, his attorneys argued in court, because of the nature of the investigation into the politically charged Plame affair. Special prosecutor Patrick Fitzgerald never proved that someone knowingly leaked to the press Ms. Plame's identity as a covert CIA employee. Indeed, no one – besides Libby – was ever charged in the case.

"The government did not establish the existence of an [underlying] offense," attorney William Jeffress said.

But the judge did not buy this line of argument. It is one thing to obstruct a petty larceny, he said. "It's another thing if you obstruct a murder investigation," said Walton.

For Libby, the outcome might have been worse. Prosecutor Fitzgerald had asked for a sentence of 30 to 37 months.

Still, the prospect of a relatively lengthy stay in jail represents a humiliating fall in stature. Libby is the highest-ranking US official to be convicted of a crime since the Iran-contra affair of the mid-1980s.

Given the opportunity to speak at his sentencing, Libby thanked Walton for his consideration throughout the trial and asked only to be judged on his whole life. He expressed no remorse about his actions – indeed, he did not refer to the actual case at all.

While the expression of remorse can lessen a sentence, Libby has also insisted that he is innocent, and he undoubtedly will appeal his conviction.

Dozens of letters from prominent people attesting to their belief in Libby's good character were entered into the record in support of his bid for probation. Among those who weighed in were former Secretary of State Henry Kissinger and former Secretary of Defense Donald Rumsfeld.